Field of the Invention
The present invention relates to a brushless core motor, and more particularly, to an improved brushless motor, of which magneto-sensitive elements (e.g. hall elements) and core windings are located in an improved relative position with each other.
In general, a brushless core motor consists of a rotor formed from a permanent magnet which produces a magnetic field, a stator including a core and armature windings on the core, and a commutating mechanism including a magnetic pole sensor and semiconductor switch. In such an arrangement, the control for electricity conduction in the motor requires provision of magnetic sensitive elements in the vicinity of the permanent magnet in order to detect the location of the magnetic pole.
In order to meet such requirements, a common brushless core motor has, for instance, the arrangement shown in FIGS. 6A and 6B, wherein hall elements 105 are each mounted at a given point on a printed circuit board 106 so that they are disposed in the vicinity of a magnet 102 secured to an inner peripheral surface of a rotor case 101 and further disposed between two adjacent salient poles 104 of a core, on which poles 104, windings 103 are wound. Such salient poles of a core will be simply referred to as "the salient poles" throughout the specification.
In another motor arrangement, as shown in FIGS. 7A and 7B, hall elements 105a are each mounted on a printed circuit board 106a such that they correspond to an imaginary salient pole 104a above the hole element 105, which pole 104a is practically cut off over its entire body as indicated by dotted lines.
However, with a motor having the arrangement in FIGS. 6A and 6B, each hole element 105 is disposed between adjacent salient poles 104, which requires the hall elements 105 to be positioned away from the core windings 103, so as to avoid contact therebetween with the result that the body of the motor is inevitably thick, and, the arrangement is not suited for use in thin motors. Even assuming no possibility of the contact between hall elements 105 and core windings 103, the disposition of the hall elements 105 close to the core windings 103 enhances a likelihood of the hold elements 105 being influenced by the magnetic flux of the core windings 103, thus involving the risk that the outputs of the hall elements 105 may be distorted. The brushless motor is constructed generally such that the outputs from the hall elements are obtained as they are to amplify them for sinewave conduction. Therefore, if the waves of the outputs from the hall elements are distorted, resultant torque ripples become so large as to deteriorate the motor efficiency and cause rough or erratic rotation of the motor.
On the other hand, the motor arrangement in FIGS. 7A and 7B has no salient pole against the hall elements 11)5, which is not satisfactory in that there is no concentration of the magnetic flux in the area of the salient pole corresponding to the hall elements 105, thus resulting in a large leakage of magnetic flux from that area towards the other side, and thereby creating unequal distribution of the leaking magnetic flux (see FIG. 5A). As a result, large torque ripples occur in the motor, or the outputs of the hall elements 105 show distorted waves (see FIG. 5B), which results in a rough motor rotation.